Fiber reinforced resin leaf springs, commonly referred to as composite springs, are used in vehicle suspension systems and are composed of fibrous material, such as glass and/or graphite fibers, bonded by a thermosetting resin. The leaf springs can be formed by filament winding processes, compression molding or pultrusion processes.
Metal leaf springs are normally connected to the vehicle axle by an axle mount construction in which the leaf spring is positioned between a clamping plate and the axle, or between a clamping plate and a pad on the axle, and U-bolts secure the clamping plate to the axle. The conventional axle mount construction, as used with metal leaf springs, cannot be used with composite springs because the rigid axle mount structure produces stress concentrations in the composite spring, particularly in the area where the edges of the clamping members engage the spring and the stress concentrations can result in premature failure of the spring.
In addition to preventing stress concentrations in the composite spring,an axle mount construction must also retain the spring in a fixed position relative to the axle under normal conditions of use. Movement of the composite leaf spring relative to the axle, or other frame member, in a direction longitudinal of the leaf spring can chyange the pivot point of the leaf spring and consequently alter the spring rate. In addition, longitudinal movement of one of the leaf springs of the vehicle will cause the axle to move out of perpendicular relation with the fore-aft centering of the vehicle, resulting in a "dog tracking" condition. Fixing the composite spring to the clamping mechanism by inserting one or more bolts through holes in the leaf spring is not a satisfactory solution for the holes sever the fibrous reinforcement and thus reduce the mechanical properties of the spring.
U.S. Pat. Nos. 4,519,590 and 4,684,110 are directed to axle mount constructions for a composite spring in which the spring is surrounded by a channel-shaped rubber or resilient insert, and the insert in turn is clamped between a pair of metal clamping members. The construction of the aforementioned patents enables the composite spring to be secured to the axle without substantially adversely affecting the mechanical properties of the composite spring.
SUMMARY OF THE INVENTION
The invention is directed to an improved axle mount construction for a composite leaf spring. In a preferred form of the invention, the axle mount construction includes a pair of metal clamping members, one of which is channel-shaped in cross section, being composed of a web and a pair of side walls that define a longitudinal channel. Flanges extend laterally from the side walls of the channel member and are disposed flat wise against the side edges of the second generally flat clamping member.
Positioned within the channel member is a pair of channel-shaped resilient inserts which in combination define a longitudinal passage that receives the central portion of the composite leaf spring. The side walls of the channel-shaped metal clamping member and the corresponding side walls of the inserts have mating concavities.
The web of the channel-shaped clamping member, as well as the clamping plate, are provided with elongated, laterally extending openings and the outer surfaces of the webs of the resilient inserts have similarly shaped projections which are recieved in the openings. The engagement of the projections with the openings acts to resist relative longitudinal movement of the inserts and spring relative to the clamping members.
As a feature of the invention, the resilient inserts project longitudinally beyond the corresponding ends of the clamping members and are tapered or feathered inwardly toward the leaf spring. The feathered ends of the inserts maintain a constant engagement with the spring surfaces during flexing of the spring and prevent dirt or foreign material from entering the clamping mechanism which could set up stress concentrations that could result in premature failure of the spring.